One way of identifying cells carrying a particular gene is by assaying for the gene product. Such products are themselves, of course, a frequent objective of genetic engineering. Most of the earliest work in genetic engineering made use of E. coli to synthesize the gene product. E. coli has the advantage that researchers are very familiar with this easily grown organism and with its genetics. It also has several disadvantages. Like other gram-negative bacteria, it produces endotoxins as part of its outer layer.
Since endotoxins cause fever and shock in animals, their accidental presence in products intended for use in humans would be a serious problem. Another disadvantage of E. coli is that it does not usually secrete protein products (Old & Primrose, 21-27). To obtain a product, cells must usually be broken open and the product purified from the resulting “soup” of cell components. Recovering the product from such a mixture is expensive when done on an industrial scale. It is more economical to have an organism secrete the product so that it can be recovered continuously from the growth of natural E.
coli protein that the bacterium does secrete. This approach has been used to produce insulin. Certain gram-positive bacteria, such as Bacillus subtilis, are more likely to secrete their products and are often preferred industrially for that reason. Another microbe that shows promise as a vehicle for the expression of genetically engineered genes is baker’s yeast, Saccharomyces cerevisiae. Its genome is only about four times larger than that of E. coli and is probably the best understood eukaryotic genome. Yeasts may carry plasmids, and their cell walls can readily be removed to introduce plasmids carrying engineered genes.
As eukaryotic cells, yeasts may be more successful in expressing foreign eukaryotic genes than bacteria. Furthermore, yeasts are likely to continuously secrete the product. Because of all these factors, yeasts have become the workhorse of eukaryotic cells. Yeasts also have a psychological advantage in the marketplace (Chilton, 50-59). Bacteria and viruses are, unfairly, associated in the public’s mind with diseases, whereas yeasts have a much more benign image, thanks to their association with baking, brewing, and wine-making.
Thesis Statement: This study gives deeper understanding of genetic engineering and its used. II. Background Animal viruses have also been used in making engineered gene products, primarily in the field of vaccine production. For example, scientists have been able to insert genes for the surface proteins of pathogenic microbes into the generally harmless vaccinia virus. The result is a sort of “sheep in wolf’s clothing,” a virus that has the external proteins of a pathogen but does not cause disease.
When an animal host is infected with the engineered virus, the host’s immune system recognizes these proteins as foreign and, in response, develops an immunity that can protect it against the cultural pathogen. Because the vaccinia virus is unusually large and has room for several extra genes, a genetically engineered vaccinia virus might theoretically be used as a vaccine for several diseases simultaneously (Barton, 40-46). Mammalian cells in culture, even human cells, can be used much like bacteria to produce genetically engineered products.
Scientists have developed effective methods for growing mammalian cells in culture as hosts for growing viruses. In genetic engineering, mammalian cells are often the best suited to make protein products for medical use; these products include hormones, lymphokines (which regulate cells of immune system), and interferon (a natural antiviral substance that is also used to treat some cancers). Using mammalian cells to make foreign gene products on an industrial scale often requires a preliminary step of cloning the gene in bacteria. Consider the example of colony-stimulating factor (CSF).
CSF, a protein produced naturally in tiny amounts by white blood cells, is valuable because it stimulates the growth of certain cells that protect against infection. To produce huge amounts of CSF industrially, the gene is first inserted into a plasmid, and bacteria are used to make multiple copies of plasmid (Barton, 40-46). The recombinant plasmids are then inserted into mammalian cells that are grown in huge tanks. Plant cells can also be grown in culture, altered by recombinant-DNA techniques, and then used to generate genetically engineered plants.
Such plants may prove useful as sources of valuable plant products, such as alkaloids (the painkiller codeine, for example) and the isoprenoids that are the basis of synthetic rubber. III. Discussion A. Its Uses • Genetically Engineered Products for Medical Therapy An extremely valuable pharmaceutical product is the hormone insulin, which is a small protein. In the mammalian body, this protein is produced by the pancreas and controls the body’s uptake of glucose from blood. For many years, insulin-deficient diabetics have controlled their disease by the injection of insulin obtained from the pancreas of slaughtered animals.
Obtaining this insulin is an expensive process, and the insulin from animals is not as effective as human insulin (Anderson & Diacumakos, 106-121). Because of the value of human insulin and the small size of the protein, the production of human insulin by recombinant-DNA techniques was an early goal for the pharmaceutical industry. To produce the hormone, synthetic genes were first constructed for each of the two short polypeptide chains that make up the insulin molecule. The small size of these chains, only 21 and 30 amino acids long, made it possible to use synthetic genes.
Each of the two synthetic genes was inserted into a plasmid vector and linked to the end of a gene coding for the bacterial enzyme B-galactosidase, so that the insulin polypeptide was coproduced with the enzyme and was secreted with it. Two different E. coli bacterial cultures were used, one to produce each of the insulin polypeptide chains. The polypeptides were then recovered from the bacteria, separated from the B-galactosidase, and chemically joined to make human insulin.
This accomplishment was one of the early commercial successes of genetic engineering and illustrates a number of the principles and procedures (Industrial Microbiology. Scientific American, 245). Another human protein hormone that is now being produced commercially by genetic engineering is somatotropin, which is also known as human growth hormone. Some individuals do not produce adequate amounts of somatotropin and are stunted in growth. In the past, growth hormone to correct this deficiency had to be obtained from human pituitary glands at autopsy (growth hormone from other animals is not effective in humans).
This practice was not only expensive but also dangerous as on several occasions neurological diseases were transmitted along with the hormone. Human growth hormone produced by genetically engineered E. coli is therefore an important product of modern biotechnology (Old & Primrose, 21-27). Earlier we mentioned a recombinant-DNA approach to vaccines by using vaccinia virus engineered to carry genes for surface proteins of a pathogen. A related approach already in use is to harvest such proteins from engineered microbial cells and then to use the purified protein as a vaccine.
The term for a vaccine consisting only a limited protein portion of a pathogen is subunit vaccine. Unlike conventional vaccines, which are killed or weakened whole micro organisms, subunit vaccines do not contain extraneous material that could cause undesirable side effects (Chilton, 50-59). • Obtaining Information from DNA for Basic Research and Medical Applications Recombinant-DNA technology can be used to make products, but this is not its only important application. Because of its ability to make multiple copies of DNA, it can serve as a sort of DNA printing press.
Once a large amount of a particular piece of DNA is available, various analytic techniques can be used to “read” the information contained in the DNA. To date, the most important achievements made possible by recombinant-DNA technology have been in basic molecular biology. Only 25 years ago, research into the detailed structures and functions of genes was extremely difficult. Now, even the complex genes of humans and other mammals are open to study (Old & Primrose, 21-27). As with all biological research, we can expect new discoveries in molecular genetics to lead to practical applications of value.
Already, recently developed techniques for DNA analysis are being used for genetic fingerprinting, which is based on the fact that the DNA of every individual is unique. In contrast to conventional fingerprinting, genetic fingerprinting requires only a few cells from the person to be identified. Furthermore, since the DNA of each species of microbe is also unique, microbiologists can use similar fingerprinting techniques to identify microorganisms, including pathogens. DNA analysis techniques are also being used to pinpoint genetic abnormalities that cause or contribute to various diseases.
These techniques are also contributing to advances in gene therapy, the replacing of abnormal genes with normal genes in a living individual (Anderson & Diacumakos, 106-121). IV. Conclusion As a conclusion, one monumental project involving much of the new technology is the human genome project, which is currently under way. The goal of this project is to map the 100, 000 or so genes in human DNA and to sequence the entire genome, approximately 3 billion nucleotide pairs. Technically, the project has been compared to the reconstruction of the contents of several sets of shredded encyclopaedias.
To reach the basic goal and to interpret the data will probably require cooperation among thousands of workers all over the world over several decades. Even before it is completed, however, the project should be immense value to our understanding of biology. It will also be of great medical benefit, especially for the diagnosis and possibly for the repair of genetic diseases. James Watson, codiscoverer of the structure of DNA, has said that, “A more important set of instruction books will never be found by human beings.
When finally interpreted, the genetic messages encoded within our DNA molecules will provide the ultimate answers to the chemical underpinnings of human existence. ”
Reference:
1. Anderson, W. F. and E. G. Diacumakos. “Genetic engineering in mammalian cells. ” Scientific American 245 (1): pp. 106-121, July 2001. Describes methods of inserting genes into mammalian cells with the goal of curing inherited diseases. 2. Barton, J. H. “Patenting Life. ” Scientific American 264 (3): pp. 40-46, March 2000. This article discusses the legal issues of ownership of genetically engineered cells.
2000. 3. Chilton, M. D. “A vector for introducing new genes into plants. ” Scientific American 248 (6): pp. 50-59, June 2003. Describes the use of the Agrobacterium Ti plasmid for genetic engineering. 4. Industrial Microbiology. Scientific American 245 (3), September 2001. An issue devoted entirely to the topic of industrial microbiology and genetic engineering. 5. Old, R. W. & S. B. Primrose. Principles of gene Manipulation: an Introduction to Genetic Engineering, 6th ed. Pp. 21-27. Boston: Blackwell Scientific, 2001.